INFERIOR MIRAGEA spurious image of anobject formed below the true position of that objectby abnormal refractive conditions along the line ofsight; one of the most common of all types ofmirage, and the opposite of a superior mirage.INSOLATION(contracted from incoming solarradiation) In general, solar radiation received atEarths surface.INSTABILITYA property of the steady state of asystemsuchthatcertaindisturbancesorperturbations introduced into the steady state willincrease in magnitude, the maximum perturbationamplitude always remaining larger than the initialamplitude.INSTABILITY LINEAny non-frontal line or bandof convective activity in the atmosphere.INVERSIONThe departure from the usual decreaseor increase with altitude of the value of anatmospheric property. The layer through which thisdeparture occurs is known as the inversion layer,and the lowest altitude at which the departure isfound is known as the base of the inversion. Theterm is almost always used in reference totemperature, but may be applied to moisture andprecipitation.KATABATIC WINDAny wind blowing down anincline; the opposite of anabatic wind. If the windis warm, it is called a foehn; if cold, it may be a fallor gravity wind.KINETIC ENERGYThe energy that a bodypossesses as a consequence of its motion, definedas the product of one-half of its mass and the squareof its speed, 1/2mv squared.LAND BREEZEA coastal breeze blowing fromland to sea, caused by the temperature differencewhen the sea surface is warmer than the adjacentland.LAPSE RATEThe decrease of an atmosphericvariablewithheight,thevariablebeingtemperature, unless otherwise specified.LATERAL MIRAGEA very rare type of mirage inwhich the apparent position of an object appearsdisplaced to one side of its true position.LIGHTVisible radiation (about 0.4 to 0.7 micron inwavelength) considered in terms of its luminousefficiency.LOOMINGAmirageeffectproducedbygreater-than-normalrefractionintheloweratmosphere, thus permitting objects to be seen thatare usually below the horizon.LOWAn area of low pressure, refer-ring to aminimumofatmosphericpressureintwodimensions (closed isobars) on a constant-heightchart or a minimum of height (closed contours) ona constant-pressure chart. Lows are associated withcyclonic circulations, and the term is usedinterchangeably with cyclone.MACROCLIMATEThe general large-scale climateof a large area or country, as distinguished from themesoclimate and microclimate.MAGNETIC NORTHAt any point on Earthssurface, the horizontal direction of the Earthsmagnetic lines of force (direction of a magneticmeridian) toward the north magnetic pole, i.e., adirection indicated by the needle of a magneticcompass. Because of the wide use of the magneticcompass, magnetic north, rather than TRUENORTH, is the common 0° (or 360°) reference inmuch of navigational practice, including thedesignation of airport runway alignment.MARITIME AIRAtypeofairwhosecharacteristics are developed over an extensivewater surface and which, therefore, has the basicmaritime quality of high moisture content in at leastit's lower levels.MEAN SEA LEVELThe average height of the seasurface, based upon hourly observation of tideheight on the open coast or in adjacent waterswhich have free access to the sea. In the UnitedStates, mean sea level is defined as the averageheight of the surface of the sea for all stages of thetide over a 19-year period.MESOCLIMATEThe climate of small areas ofEarths surface that may not be representative of thegeneralclimateofthedistrict.Theplacesconsidered in mesoclimatology include smallvalleys, frost hollows, forest clearings, and openspaces in towns, all of which may have extremes oftemperature differing by many degrees from thoseof adjacent areas. The mesoclimate is intermediateinscalebetweenthemicroclimateandmicroclimate.MESOPAUSEThe top of the mesosphere.Thiscorresponds to the level of minimum temperature at70 to 80 km.AI-4